Foldable and retractable endless track type landing gears



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NVENTO ALFREIb A. GAS

June 13, 1950 A. A. GASSNER 2,510,969 FOLDABLE AND RETRACTABLE ENDLESSTRACK TYPE LANDING GEARS v Filed Feb. 25, 1949 3 Sheets-Sheet 2 June 13,1950 A. A. GASSNER FDLDABLE AND RETRACTABLE ENDLESS TRACK TYPE LANDINGGEARS 3 Sheets-Sheet 5 Filed Feb. 23, 1949 INVENTOR FIG. 3.

Patented June 13 1950 FOLDABLE AND RETRACTABLE ENDLESS TRACK TYPELANDING GEARS Alfred A. Gassner, NewYork, N. Y.,"assignor to FairchildEngine and Airplane Corporation, New York, N. Y., a corporation ofMaryland Application February 23, 1949, Serial No. 77,754

15 Claims. (01. 244*102) This invention relates to retractable landinggear for aircraft and has particular reference to and endless track typeof landing gear; which is foldable and retractable for compact stowageafter retraction within the body of the aircraft and constitutes animprovement in the gear disclosed in copending application Serial No.45,597, filed August 23, 1948, now Patent 2,497,880, issued February 21,1950.

As stated in said copending application, an increase in the overallweight of the aircraft requires a proportional increase in the trackprint area until for large and heavy craft such as cargo aircraft, thegear must be inordinately large in order to provide track print areas ofa size to keep the ground pressure down to a safe value of between aboutand 28 pounds per square inch static loading. Inasmuch as the width ofthe stowing nacelle limits the track width, it becomes necessary toincrease the track length in order to maintain the required track printarea. But when the track length is thus increased, retraction of thegear becomes practically impossible since the nacelle space of existingaircraft is too short to accommodate a long track, thus requiringaircraft redesign, which is usually not feasible since standard modelsare desired and should be adaptable without material change for use onlanding fields with usual tricycle landing equipment, as well as forspecial uses as here described, merely by fitting them with the properlanding gearfor the required service. The landing gear disclosed in saidcopending application meets these requirements and includes a separatecable retracting element to give the last contraction before retractioninto the nacelle. The present instill be fully maneuverable underadverse condi; tions. 1

In a preferred embodimentof the invention, the endless track gear isprovided. with an extra ground-engaging idler roller or bogie aboutwhich the track belt may fold and the bolster or frame of the endlesstrack gear is divided about a horizontal transverse axis, the front partof the frame carrying the front wheel or bogie assembly being pivotableupwardly about that axis by a hydraulie cally-actuated linkage to causethem and part of the track belt to move bodily rearwardly and upwardlyupon the rear portion of the gear so that the gear assumes a generallyc-shaped configuration, with the result that the overall length of the.track is materially decreased from its normal extended position. Thenthe gear is movedbodily upwardly on parallel struts without rotationwhile in that C-shaped position and condition into the stowage nacellewherein it reposes dur-. ing flight. ,1

It will be seen that by means of the compact ly foldable landing gear ofthis invention, material redesign of existing aircraft becomesunnecessary in order to accommodate landing gear having sumciently lowground pressure per square inch of track print surface to permit oper-'ations to, over and from the afore-mentioned uning drawings in which:

Figure 1 illustrates the foldable 3 of this invention shown both in thefull ground vention provides a gear vwhich is foldable into a stillsmaller compartment without the aid of an auxiliary cable.

In accordance with the present invention, an

contact position for static and taxiing purposes,- and in dotted linesin' the retracted and folded position within the stowage nacelle;

' I Fig. 2 shows the gear in folded position; and

endless track .type landing gear for even the largest known aircraft isprovided, which is retractable into the stowage space of the aircraftand which affords the desirably low. ground pressure of about 25 to 28pounds per square inch in order to have the advantages of smaller,trackequipped aircraft, of maneuverability over, landing on and take-offfrom soft and irregular terrain. Thesedesirable attributes are largelyprovided by the foldability of the gear before retraction intoa smallsize and uniform shape, enabling itrtor be retracted into a relativelysmall rectangular nacelle space .of cargo aircraft of existing design fostowage during flight, whereby existing 'cargo craft may' be veryheavily loaded and Fig. 3 is a front view of the gear in extendedposition as seen in partial sectional view along the line 3-3 of Fig. l.i. Inthe ensuing description, the near side of the gear will bedescribed, it being understood that the other, or far side, is the same.Referring to Fig. 1, the bolster or frame. I0 is divided into a main orfixed rear portion I0 and the movable or front portion ID, thearticulation of these portions to be described. Front portion III, ofthe frame l0 carries at its forward end the horizontal shaft I I aboutwhich are pivoted two bell cranks l2 and I3, both at the free ends oftheir upper arms l2 and [3, respectively. Bell crank l2 carries at itselbow the horizontal shaft [4 for the frontidler wheel 'or bogie t5which is fully ele-. vated above the ground surface G when the gearretracting gear the rear axle 23 upon whichthe rear wheel or bogie 24 isjournalled through the intermediary of an eccentric 25 whereby the track26 encircling wheels or bogies I5, 20 and 24- isautomaticallyl tightenedto tension the track-upon application of the brake 21, as is describedmgreater detail in copending application Serial No. 37,628g filed July;j V

4 sure fluid is supplied through valve V into lower port 52 of powercylinder 50, the reverse or unfolding operation occurs. The hydraulicsystem is preferably constructed like that disclosed in said copendingapplication Serial No. 45,597.

Secured on pivotal yoke 43 is the horizontal bar on whose-oppositef-reeends are mounted the bolsters largely constituting the rear frame 10 andincluding the intermediate bolsters 55 so that the entire frame If!composed of the relatively stationary rear portion and the pivoted'rb'rw'ara portion It! may tilt laterally to an ex- "tntlimit'ed byauxiliary struts 58 extending be- 8, 1948, now Patent 2,504,128, issuedApril 18,

The forward end 22 of the rear horizontal lever 22 is pivotedtothe-cylinder of a vertical shock strut 28 whose piston rod 28' ipivoted to the approximate center of a substantially horizontal lever 29at whose opposite free ends are journalled the two intermediate groundengazing wheels or bogies'Sli. The front frame portion isrigidly-secured ona; cross-shaft .32 journalled in rear frame-pom tien Wso that front frame portion 10" may move in an upward and rearward arcto swing the front bell cranks l2 and 13' upwardly and rearwardly in themanner shown particularly in Fig. 2.

A third shock strut 31' is connected betweena lever 32 fixedoncross-shaft 32 and a lever I9 connected to the elbow of bell crank lever13, as

shown. 7 y

A fourth shock strut 33 also is secured to rear frame M with its pistonrod 34 pivoted intermediate the ends ofa lever 35 pivoted on: rear frameportion I0 and carrying an axle 36 of a third idler wheel or bogie 31about which the track "folds upwardly and rearwardly when front frameportion in is pivoted in that directionjas shown in Fig. 2.

Rigidly secured on shaft 32 is a lever 38' whose free end is pivotallyconnected to a link ieintum pivoted by pin4tto the second-link 41connected by pin 42 to a yoke 43 journalled on a-fore an'de. aft. stubshaft l4, carried by the cantilever-casting 45 onthe' lower end of thepiston 46 of themain load carrying shock absorber strutA-l supported bytransverse pivot pin 48 on the air frame F. Also carried by the yoke 43so as to be tiltable with it about fore and-aft pivot 44 is a bracket 49carrying the power cylinder 50 whose piston rod is pivoted to the pin-48 connecting theaforee mentioned links 3! and 40, which accordinglyform a toggle.

Suitable hydraulic control means connected to respective upper and lowerports 51 and 52 extend and retract the power cylinder 58; i. e, whenhydraulic fluid under pressure is supplied by pump P to upper port if bymanipulation of valve V by the operator, cylinder 50 is extended todrive toggle links 3! and 4| downwardly,- therebyc'ausing lever 38 torotate cross-shaft 32 and raise the front frame portion 10 upwardly andrearwardl-y about the axis of cross-shaft 32. As shown particulariy by2, bogies or wheels 15 and 2G and the, forward portion of track 26 arecarried with front frame 40 so that the track 26 is folded back onitself about idler bogie 28 at its lower course and at its upper courseaboutfa cross-roller 53 carried by yoke 43. When the hydraulic prestweenthe'horn- 51- on the forward portion l0" j of theframe and-apivot point58 on the air frame F1 The" bodily rotation of the frame 10 andconsequently of the landing gear itself about horizontal fore-and-aftaxis 44 is limited in this fashiorr'to approximately 10 at either sideof horizontal, as is indicated in dotted lines in Fig. 3, and issufiicient toenable the: gear to accommodate" obstructions. unevenground and other irregularities during taxiing, take-off andvlandlna.

alhe afore-mentioned: auxiliary shock struts 5| extending from pivotpoints 58 on the air frame F to pivot points 69 on the horn 51 of therear frame portion Ht"v aid-mainstrut 4"! in transmitting the weight ofthe airplane to the track gear under normal landing, taxiing and staticconditions of the craft. When the airplaneis in the air, struts- 41- andlili extend to the limit of their length and the trackgear assumessubstantially the position shown by the dot-and-dash lines in Fig. 1. Alinkage: 59 extends between pivotpoint 60 onpiston casting 45 and pivot51- on the lower end of the cylinder 46 of shock strut 41 tomaintainthe. track oriented. parallel to the fore-andaft axis-of theaircraft. 1 The: lower portioneof the necelle NY in the air fram'e Fopen and within it is located the retracting mechanism for the gear,which is addi time! to and to a certain extent, independent of the trackfolding mechanism just described. It includes a link 62, connecting thelower end of the shock strut ll by 9; cross-pin 63', to which areconnected the lower ends-ofapair of links 64 pivoted at their. upperends on pins 65.130 the air frame F within the naoelle N Also pivoted atpoint 66 on the-air frame withinuthe necelle N is the main retractionactuating stmt '61 connected at its lower end 68 to the links 64 andbeing. adapted to extend and retract hydraulically by the admissiontol'opposite'sides' of the piston of pressure fluid-controlled by avalve in a" manner well understood and disclosed in detail in saidcopending application Serial No. 45,597.

in operation oithe landlnggear of this invention, and considering thefolding operation, immediately after take-off of the aircraft, theoperator moves the control valve to admit pressure fluid to the inletport. 5t of the folding actuating strut St -thereby causing it to extendfrom the shortened length shown in Fig. 1 to the extended length'shownin Fig 2. The extension of the actuating strut forces-links 39 and 41downwardly,- thereby causing lever 38 to be rotated clockwise about theaxisof-cross-shaft 32. Inumnch as lever 3 is rigidly fastened oncrossshaft Bijoumalled in the front end of rear frame portion ll", andas the forward frame portion H rigidly secured to shaft 32, it isrotated upwardly and rearwardly by lever ll about the axis of shaft 32.from the position shown in Fig. l to the position inil ig. .2. Inasmuchas the for- Wandframe portion It! carries the bell cranks l2 and 13 onwhich front wheel I and front idler wheel 20 are mounted,these wheels l5and 20 also move upwardly and rearwardly with forward frame portion Ill"carrying the corresponding part of the track26 with them, which foldsabout idler wheel or bogie 31, as shown. By reason of the roller 53extending across the upper surface of the upper course of the track 26,the track is folded about roller 53 in the manner shown in Fig. 2.

Inasmuch as the lower ends of struts 56 are connected to the horn 51 ofthe relatively stationaryrear frame portion they do not swing during thefolding operation, nor does main shock .strut :41, although bothlengthen as shown in v2 because they have been relieved of the static ortaxi load and are pulled out by the weight of the gear. It will beobserved that struts 41 and '56 are substantially .parallel.

Following the folding and rotation of the entire track assembly :to theposition shown in Fig. v2, as described, the operator moves the controlvalve to retraction position, which pumps pressure fluidnto retractionactuating strut B1 to cause it to extend to fold links 56 abouttheir'pivot points "58 and draw frame 10 upwardly with them. At the sametime, the main load strut 41 swings forwardly and upwardly about itspivot point 48 so as to raise the entire gear without substantialrotation, from the Fig. 2 position into the nacelle N in the mannerindicated in dotted lines in Fig. 1. Because the supporting struts 41and 56 are substantially parallel, theentire gear moves upwardly in anattitude which remains substantially parallel to itself withoutsubstantial rotation as stated. It will be understood that the gear islocked in folded, unfolded, retracted and extended positions by thehydraulic fluid pressure in actu- .ating cylinders 50 l and 61.

In extending the gear from the stowed position shown in dotted lines inFig. l, to the landing position also shown in Fig. l, theafore-mentioned hydraulic power cylinders 50 and 61 will be operatedin-reverse sequence, first to supply the main retracting strut 61 withpressure fluid to shorten the same and lower the gear to the foldedposition shown in Fig. 2 and-to supply the lower port 52 of the foldingactuating strut 50 to shorten the same from the length shown in Fig. 2to that shown in Fig. l to effect the unfolding of the gear from thefolded shape shown in Fig. 2 to the fully extended shape shown inFig. 1. It will be understood that the operation of the several parts iseffected in the reverse order from that previously described inconnection with folding and lockingprior to retraction.

when the gear is extended to the position shown in Fig. l, the aircraftis ready to land, the rear end or heel of the track 26 engaging theground first by reason of the lower position of the rear bogle 21,as-shown in dotted lines in Fig. 1. As the :rear of the track engagesthe ground, the main -load strut 41 contracts on impact and the gearswings about horizontal pivot 54 in a counterclockwise direction untilthe full track print engages the-ground as shown'in solid lines in Fig.l,

the track meanwhile adjusting itself laterally about fore-and-aft pivot44 in the manner indicated in Fig. 3 to accommodate lateral unevennessof the ground.

It will be understood that two or more of the landing gear illustratedand described will be used oneach aircraft,-or one of them with pilotwheels, and the like, depending upon requirements. Also, thelnose gearmaybemade steerable ina suitable '6 manner, and the control mechanismmay bemade automatically sequential in the manner described insaidcopending application Serial No. 45,597.

Although a preferred embodiment of the fold.- ing endless track gear hasbeen illustrated and described herein, it is understood that the inven!-tion is not limited thereby nor is this folding track limited to use onairplanes, but is susceptible of other uses and to changes in form anddetail within thescopeof the appended claims.

I claim:

1. In aircraft landing gear .of theendless track type having alongitudinal frame, front and rear wheels carried thereby and an endlessbelt encircling said wheels, the combination of hinge means dividingsaid frame transversely into aligned front and rear portions, means forfolding one frame portion relatively to the other portion to collapsethe gear, substantially parallel link means pivotally connecting saidframe to the aircraft about corresponding parallel axes, and means forswinging said collapsed gear bodily parallel to itself about saidparallel axes.

2. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheelscar-ried thereby and an endlessbelt encircling said wheels, the combination of hinge means dividingsaid frame transversely into aligned front and rear portions, means forfolding one frame portion relatively to the other portion to collapsethe gear, substantially parallel link means pivotally connecting saidframe to the aircraft about corresponding parallel axes, and motivemeans for swinging said collapsed gear bodilyparallel to itself aboutsaid parallel axes.

3. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carried thereby and an endlessbelt encircling said wheels, the combination of parallel spacedstrutsextending downwardly from the aircraft and'pivoted abouthorizontal pivots thereon, substantially horizontal transverse pivotsconnecting said frame to said struts, hinge means dividing said frametransverselyinto aligned front and rear portions, motive means forswinging said frame portions relatively to each other about said hingemeans to at least partiallyfold one frame portion on the other, andmotive-means for swinging said folded frame portions bodily parallel toitself on said struts about said pivots.

4. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carried thereby and an endlessbelt encircling said 'wheels, the combination of hinge means dividingsaid frame transversely into aligned front and rear portions, motivemeans for swinging said front frame portions upwardly and rearwardlyabout said hinge means to at least partially fold said first frameportion upon the rear frame portion, substantially parallel-link meansconnecting said rear frame portion to the aircraft about correspondinghorizontal axes, and motive means to swing said folded gear bodilyupward substantially parallel to itself about said horizontal axes.

5. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carried thereby and an endlessbelt encircling said wheels, the combination of parallel spaced strutsextending downwardly from the aircraft and pivoted about horizontalpivots thereon, substantially horizontal transverse .pivots connectingsaid frame to said struts, hinge means dividing said frame transverselyinto aligned front and rear portions, motive means carried by said'framefor swinging said frame portions relatively to each other about saidhinge means to at least partially fold one frame portion on the other,and motive means for swin ing said folded frame portions bodily parallelto itself on said struts about said pivots.

6. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carried thereby andan endlessbelt encircling said wheels, the combination of parallel spaced strutsextending downwardly from the aircraft and pivoted about horizontalpivots thereon, substantially horizontal transverse pivots connectingsaid frame to said struts, hinge means dividing said frame transverselyinto aligned front and rear portions, motive means carried by said rearframe portion for swinging said frame portions relatively to each otherabout said hinge means to at least partially fold one frame portion onthe other, and motive means for swinging said folded frame portionsbodily parallel to itself on said struts about said pivots.

7. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carried thereby and an endlessbelt encircling said wheels, the combination of hinge means dividingsaid frame transversely into aligned front and rear portions, motivemeans carried by said rear frame portion for swinging said front frameportions upwardly and rearwardly about said hinge means to at leastpartially fold said frame portion upon the rear frame portion,substantially parallel link means connecting said rear frame portion tothe aircraft about corresponding horizontal axes, and motive means toswing said folded gear bodily upwardly substantially parallel to itselfabout said horizontal axes.

8. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carrier thereby and an endlessbelt encircling said wheels, the combination of substantially parallelspaced struts pivotally connecting said frame to the aircraft, hingemeans dividing said frame transversely into aligned front and rearportions, motive means carried by one of said frame portions forswinging said frame portions relatively to each other about said hingemeans to at least partially fold one frame portion upon the other, andsecond motive means interposed between the aircraft and said struts forswinging said gear bodily upwardly parallel to itself upon said strutsinto a retracted position.

9. In aircraft landing gear of the endless track type having alongitudinal frame, front and rear wheels carried thereby and an endlessbelt encircling said wheels, the combination of substantially parallelspaced struts pivotally connecting said frame to the aircraft, hingemeans dividing said frame transversely into aligned front and rearportions, motive means on said rear frame portions for swinging saidfront frame portion upwardly and rearwardly about said hinge means to atleast partially fold said front frame portion upon said rear frameportion, and second motive means interposed between said gear, saidstruts and the aircraft for swinging said gear upwardly parallel toitself upon said struts into a retracted position.

10. In endless track gear of the type having a longitudinal frame, frontand rear wheels carried therebyand an endless belt encircling saidwheels, the combination of hinge means divided said frame transverselyinto aligned front and 'journalled in said rear frame portion andrigidly secured to said front frame portion for movement therewith, alever secured to said shaft, a toggle interposed between said lever andsaid rear frame portion, a hydraulic cylinder and piston combinationconnected at one end to said toggle and pivoted at the other end on saidrear frame portion, and means for supplying fluid under pressure to saidcylinder for actuating. the piston therein to thereby cause said pistonto swing said front frame portion, the corresponding front wheel and thecorresponding section of the belt to and from at least partially foldedposition over said rear frame portion. 1

11. In endless track gear of the type having a longitudinal frame, frontand rear wheels carried thereby and an endless belt encircling saidwheels, the combination of hinge means dividing said frame transverselyinto aligned front and rear portions, said hinge means including a shaftjournalled in said rear frame portion and rigidly secured to said frontframe portion for movement therewith, a lever secured to said shaft, atoggle interposed between said lever and said rear frame portion, ahydraulic cylinder and piston combination connected at one end to saidtoggle and pivoted at the other end on said rear frame portion, a sourceof fluid under pressure to said cylinder for actuating the pistontherein, and a valve in said connections for controlling the flow ofpressure fluid to said cylinder to thereby cause said piston to swingsaid front frame portion, the corresponding front wheel and thecorresponding section of the belt to and from at least partially foldedposition over said rear frame portion.

12. In endless track' gear of the type having a longitudinal frame,front and rear wheels carried thereby and an endless belt encirclingsaid wheels, the combination of hinge means dividing said frametransversely into aligned front and rear portions, a toggle connectingsaid rear portion to said front portion at a point spaced from saidhinge, and motive means carried'by one of said frame portions andconnected to said toggle for swinging said front frame portion upwardlyand rearwardly about said hinge means to at least partially fold saidfront frame portion, the corresponding wheel and the corresponding beltsection upon the rear frame portion and its appurtenant wheel and beltsection.

13. In endless track gear of the type having a longitudinal frame, frontand rear wheels carried thereby and an endless belt encircling saidwheels, the combination of hinge means dividing said frame transverselyinto aligned front and rear portions, a toggle connecting said rearportion to said front portion at a point spaced from said hinge, motivemeans carried by one of said frame portions and connected to said togglefor swinging said front frame portion upwardly and rearwardly about saidhinge means to at least partially fold said front frame portion, thecorresponding wheel and the corresponding belt sec-, tion upon the rearframe portion and its appurtenant wheel and belt section, substantiallyparallel struts connecting said frame -by horizontal pivots to theaircraft, and motive means connected to said struts for bodily swingingsaid frame upwardly parallel to itself into retracted position.

14. In endless track gear of the type having a longitudinal frame, frontand rear wheels carried thereby and an endless belt encircling said rearportions, said hinge mea including a shaft wheels, the combination ofhinge means dividing said frame transversely into aligned front and rearportions, motive means for swinging said front frame portion upwardlyand rearwardly about said hinge means to at least partially fold saidfront frame portion, the corresponding wheel and the corresponding beltsection upon the rear frame portion and its appurtenant wheel and beltsection, an intermediate ground wheel mounted on said rear frame portionand extending across the inner surface of the belt at a pointsubstantially opposite said hinge means about which the belt is foldedduring the said swinging movement of said front frame portion.

15. In endless track gear of the type having a longitudinal frame, frontand rear wheels carried thereby and an endless belt encircling saidwheels, the combination of hinge means dividing said frame transverselyinto aligned front and rear portions, motive means for swinging saidfront frame portion upwardly and rearwardly about said hinge means to atleast partially fold said front frame portion, the corresponding Wheeland the corresponding belt section upon the rear frame portion and itsappurtenant wheel REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,552,283 Elder Sept. 1, 19252,169,443 Burke Aug. 15, 1939 FOREIGN PATENTS Number Country Date754,073 France Aug. 21, 1933 Certificate of Correction Patent No.2,510,969 June 13, 1950 ALFRED A. GASSN ER It is hereby certified thaterror appears in the printed specification of the above numbered patentrequiring correction as follows:

Column 7, line 32, for the words said frame read said first frame; line41, for carrier read carried; line 73, for divided read dividing;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOffice. in, Signed and sealed this 10th day of October, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommz'ssioner of Patents.

